A false positive case of high-sensitivity cardiac troponin in a patient with acute chest pain: Analytical study of the interference

We report a case of a heterophile antibodies interference in a new high-sensitivity troponin commercial immunoassay (cTNIH Siemens), observed in a patient with possible acute coronary syndrome (ACS). The analytical interference was investigated with standard laboratories procedures. The false positive result was found with different troponin methods and kits. We also investigated the protein sequence of cTnl and no sequence variants were detected. The discordance between clinical pictures and high concentration of cTnl, together with the collaboration between clinicians and laboratory staff avoided possible erroneous diagnosis and further invasive investigations to the patient.

Clinical use of cardiac troponin for acute cardiac care and emerging opportunities in the outpatient setting

Cardiac troponin (cTn) testing has evolved significantly in recent times. Because of increased sensitivity, its use has shifted from a marker used to help diagnose acute myocardial infarction (MI) to a marker than can be used in the outpatient setting, as well as for both detection of myocardial injury and risk-stratification. Its main role remains in the diagnosis of acute MI and the risk-stratification of patients presenting with suspected acute coronary syndrome. The analytical improvements in assays leading to precise high-sensitivity cTn assays have contributed to the development of numerous strategies to identify patients at both low- and high-risk for acute MI within a few hours. These approaches should reduce overcrowding in the emergency room and expedite triaging. The ability of measuring cTn in most patients using high-sensitivity (hs) assays has allowed for the opportunity to examine its use in the detection of cardiotoxicity in patients undergoing chemotherapy, as well as exploring the application in both primary and secondary prevention of coronary artery disease. This particular field of research has become increasingly complex, partly due to the numerous cTn assays available (I and T; point-of-care, contemporary, hs) and an array of approaches in which one can use the test. The purpose of this document is to summarize the analytical and clinical information relevant to cTn assays, in particular, hs-cTn assays, and describe present and future opportunities for use of cTn in acute cardiac care and in the outpatient setting.

Multi-centre evaluation of recent troponin assays for the diagnosis of NSTEMI

Objectives

We aimed to compare the use of nine different cardiac troponin (cTn) assays (2 cTnT and 7 cTnI) for the diagnosis of NSTEMI in a single multi-centre population.

Design and methods

One hundred and fifty-eight patients were included (mean age 60 years, SD 17 years), including 23 patients (14%) with NSTEMI.

Results

The analytical comparison highlighted a large heterogeneity of cTn assays, as reflected by percentages of patients with detectable cTn, correlation coefficients, Passing-Bablok comparisons and concordance coefficients. Correlations within cTnI assays were good and correlation within cTnT assays was excellent. Diagnostic performances demonstrated that each cTn assay has specific threshold values. Furthermore, some assays (HS-cTnI and T, cTnI-Pathfast and cTnI-Centaur) indicated high sensitivity and negative predictive value using the limit of detection (LoD) diagnostic strategy. For the latter assays, a significant increase in specificity was found when using the 99th percentile or the H0-H3 strategies, in comparison to the LoD strategy. When applying the European Society of Cardiology H0-H3 algorithm, comparable diagnostic performances were obtained.

Conclusion

All 9 cTn assays indicated overall good diagnostic performances for the diagnosis of NSTEMI in emergency departments when the recommended algorithm based on the variation of cTn value between two measurements at admission and 3 h later was used.

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We compare nine troponin assays for the diagnosis of NSTEMI.

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Each cTn assay owns specific thresholds for the ESC H0-H3 algorithm.

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All assays present high specificity for NSTEMI diagnosis using H0-H3 algorithm.

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Assay-specific threshold and delta change values for each cTn assays are mandatory.

How is cardiac troponin released from injured myocardium?

Cardiac troponin I and cardiac troponin T are nowadays the criterion biomarkers for the laboratory diagnosis of acute myocardial infarction due to their very high sensitivities and specificities for myocardial injury. However, still many aspects of their degradation, tissue release and elimination from the human circulation are incompletely understood. Myocardial injury may be caused by a variety of different mechanisms, for example, myocardial ischaemia, inflammatory and immunological processes, trauma, drugs and toxins, and myocardial necrosis is preceded by a substantial reversible prelethal phase. Recent experimental data in a pig model of myocardial ischaemia demonstrated cardiac troponin release into the circulation from apoptotic cardiomyocytes as an alternative explanation for clinical situations with increased cardiac troponin without any other evidence for myocardial necrosis. However, the comparably lower sensitivities of all currently available imaging modalities, including cardiac magnetic resonance imaging for the detection of particularly non-focal myocardial necrosis in patients, has to be considered for cardiac troponin test result interpretation in clinical settings without any other evidence for myocardial necrosis apart from increased cardiac troponin concentrations as well.

Using High-Sensitivity Cardiac Troponin T for Acute Cardiac Care

The recent approval of the fifth-generation cardiac troponin T assay, which has characteristics clinically of a high-sensitivity assay, has led to concern that the problems of increased sensitivity will be greater than the benefits. This will not be the case if cardiology, emergency medicine, and laboratory medicine combine to develop procedures for use of the assay. We advocate sex-specific 99th percentile upper reference limit values of 15 ng/L for men and 10 ng/L for women. We suggest a 2-hour rule-out strategy, including a value less than the 99th percentile upper reference limit and the lack of a change in values of <4 ng/L. Those with values >100 ng/L and or a changing pattern of values ≥10 ng/L are a population much more likely to have acute myocardial infarction. Most of the increment in elevated values will occur not in those with acute coronary problems but in those with primary cardiac disease like heart failure and those with primary noncardiac problems. The former belong on a cardiac service because they are at high risk. The latter should have therapy on the service most apt to provide optimal care for their primary diagnosis, with cardiac consultation as needed.